(a) Field of the Invention
The present invention relates to a polarization control device and method and, more particularly, to a polarization control device and method using a polarization converter.
(b) Description of the Related Art
An optical fiber has an advantageous characteristic in terms of high-speed and long-distance transmission of a signal because it has a small transmission loss and can transfer a wideband signal as compared with a cable or a coaxial cable using a copper wire. Furthermore, an optical fiber is used a lot in photosensors in addition to optical communication because the connection of an optical signal to the optical fiber is easy and simple. Polarization is one of the characteristics of an optical signal, and a polarization state (e.g., a shape of polarization or an angle of polarization) of an optical signal passing through an optical fiber is changed by birefringence within the optical fiber. The amount of birefringence within an optical fiber is changed by a change of temperature, pressure, or bending. The amount of birefringence within an optical fiber is small, but the direction of birefringence within an optical fiber is not regular and the amount of birefringence within an optical fiber is changed by its location. A polarization-maintaining optical fiber designed to maintain its polarization state by intentionally increasing birefringence within the optical fiber has been developed, but is not used a lot. Since an optical fiber used in optical communication or photosensors has specific birefringence and the optical fiber is changed over time as described above, an output polarization state of the optical fiber is also changed over time when an optical signal passes through the optical fiber.
Meanwhile, in an optical communication or photosensor system using the polarization characteristic of an optical signal, a polarization state of a received optical signal needs to be maintained regularly. If a polarization state is not maintained regularly, the amount of a received signal can decrease or disappear because the polarization state is changed.